Halftone photoengraving process



1 1945- w. s. MARX, JR 2,373,489

HALFTONE PHOTOENGRAVING PROCESS AND SCREEN Filed Oct. 18, 1941 .331 5 1wlllliiill i lilim ll": l I I I .MIIIM ||||ll Q ||l..

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Patented Apr. 10, 1945 nALrroNs PHOTOENGRAVING PROCESS w Ann SCREEN 1'Walter S. Marx, J12, Santa Barbara, Calif., as-

signor to Printing Arts Research Laboratories, Inc., Santa Barbara,Calif., a corporation of Delaware Application October 18,1941, SerialNo. 415,530

7 lClaims.

This invention relates to an improved halftone photoengraving processand an improved halftone screen for use in such process.

One of the objects of the invention is to provide to give printedillustrations which are characterized by the absence of screen patternin the highlights, by clean solid lines and type devoid of screenpattern, and shaded portions which are reproduced with thaid of thescreen pattern as dots depending for sizeupon the shading of theoriginal artists drawing. In other words, by the aid of this screen andthis process, I am enabled to make reprodnctions of artists drawings in.

which the shaded portions are reproduced in substantially conventionalhalftone photoengraving manner but in which lines and type are free fromscreen pattern and in which the highlights are completely free fromscreen pattern.

By a slight modification of my process, I are enabled to introduce aslight amouht of screen pattern into the solid portions of the printingplate while at the same time preventing encroachment of screen patternupon the line and type elements.

An artists drawing comprises the following elements; First there issolid color which will hereinafter he referred to by this term. Second,there are highlights which are free from pigmerit. Third, there areshaded portions which differ in degree of intensity of the pigment.Fourth, there is line. Line" can be regarded solid color of small width;Nevertheless, wing to the fact that it is preferred in printing platesto have a small degree of screen pattern in solid color,. and furtherowing to the fact that one of the principal objects of the presentinvention is to prevent the occurrence of screen pattern in line, it isnecessary clearly to dii ferentiate between these two elements of adrawit will be understood 'that line is intended to include solid lineswhich the artist may use in making the drawing and also legends,numbers, and the like, which are referred to briefly as"type.

In generaltenns, my invention involves the employment of two differentkinds of light or, to he more enact, lighting of two ranges of wavelength. The plates employed are sensitive to both kinds of light. Myimproved screen is provided with rulings or pattern composed of lineswhich are transparent or substantially transparcut to one kind of light,while they are opaque to the other kind of light. The drawing .or me.-

lit

terial to be reproduced is either prepared or treated so that the shadedportions thereof are made opaque to that kind of light for which thescreen pattern is transparent.

In actual practice it is preferred to employ visible and ultra-violetlight as the two kinds of light and it is further preferred to make thescreen with lines or pattern which are transparent to ultra-violet lightand which are efiectively opaque to visible light, or, more particularlyto visible light having substantial actinic effect upon the photographicplates employed in the photoengraving process.

The employment or ultra-violet and ordinary light is particularlyadvantageous in the preparation of the drawing, since the artist can, aswill hereinafter he explained, employ pigments and colors which appearthe eye similarly to pigments and colors heretofore used. The pigmentsor colors may, however, as will hereinafter be described, containmaterial which renders them quite opaque to ultra-violet light.Consequently, the shaded portions will be quite onaque to ultra-violetlight although to the eye of the artist, or indeed to the eye of anyobserver, they appear to he normal shaded The drawing prepared in thiscolor" and line hath of which opaque to both visible and t lt However,the shaded portions? opaque to ultra-violet light. 1 t of the process, anegative is pre aid of the screen and with the violet and visible light.As indicated alcove, my improved p-rocessir revents occurrence of screenpattern in the line, and unless additional steps are taken, the s dcolor" will likewise be devoid oi screen Since this is frequentlyconsidered objection r printing purposes, additional steps may men to f-rovide screen pattern in the "solid color while maintaining the linedevoid oi such pattern.

Other objects, advantages and capabilities of the invention will appearfrom the following" spe cific description of preferred embodimentsthere-- of taken in conjunction with the aeccompanying drawing in which:

Fig. l is a plan view of a screen embodying my invention;

Fig. 2 is a plan view of one which my screen is fabricated;

Fig. 3 is a cross-section of plate shown in 2; t

Fig. 4 is a similar cross-section of the modified has solid clacl: orviolet light.

tlalll the plates from formof plate;

which is to been greatly enlarged from small portions of a drawing andnegatives actually produced photographically. Indeed, all the iigures'ofthe.

drawing are greatly enlarged.

My improved screen which is shown in Fig. 1

asraasc it in the form of dyed gelatine upon the surface of the glassplate. It may herebe noted that if gelatine is used for the base of theline it, a water solution of fuchsine will dye it. In the case of theother plastic materials mentionedya water and alcohol solution offuchsine may advantageously be emmay suitably consist of two sheets ofglass which support between them lines it and ii of material which issubstantially opaque to the actinic portion of ordinary light and whichis substantially transparent to ultra-violet light. The lines i0 andiiare arranged in intersecting relation and they are preferably locatedat right angles.

to each other and in oblique relation to the major dimensions of thescreen.

The two. sheets of glass'are secured together Ployed.

It is to be noted that whil I have successfully used fuchsine, it willbe understood that any other clye,'or indeed any other material whichtransmits ultra-violet light and is substantially opaque 'to actinicvisible light, may hev used instead of i'uchsine.

It will or course be understood that materials other than -fuchsine maybe employed. Other materials which are efiectively transparent to withthe aid of Canada Balsam or other suitable cement, or with the aid ofany'other suitable securing means, so that the lines it and ii are incontact and in sandwich relation to the two sheets of glass.

In Fig.- 2 I have shown one sheet of glass having the lines is thereon.The lines to and it Referring to the embodiment of Fig. '3, the

grooves 052 may be-rnade with a diamond cuttin device, the depth of thegrooves being suficient to allow for a deposit of a transparent resin orgelatinous material capable of transmitting near ultra-violet light,while absorbing visible actinic light.

Gelatin or polymerized methyl-methacrylate, commonly known as Lucite, orPlexiglass, or indeed any medium which is transparent to ultravioletlight and which will carry the dye employed, may be used as a iillingmedium for the grooves it. These materials may be dyed with a pure gradeof fuchsine and they then transmit light below 4,000 angstrom units andefi'e'ctually absorb light between 4,000 and 6,000 angstrom j venientlyformed photographicaily from a master screen. The first step is toexpose and develop aphotographic plate so that the screenrulings appearas a silver image in the gelatine. A suitable dye such as iuchsine issubstituted for the reduced silver in thegelatlne coating on the plateby methods known in the art. The remaining undyed gelatlne maybe eitherremoved or.

allowed'to remain between the dyed screen lines.

In Fig. 4 the gelatine in"whi ch the silver was not reduced is shownremoved, leaving only the lines.

ultra-violet light-and-eflectively opaque to the actinic portion ofordinary light includenitroso-dimethylaniline, methyl violet, glass orgelatine suspensions of nickel and cobalt salts, and suspensions ofcobalt chloride, copper sulfate, acetamine scarlet B.

It will be understood that the lines i0 and H may be of any desirednumber as in conventional screens. Thus, the number of lines may be be-'tween 50 and 300m the inch. r

The. artists drawing, a fragment of which is; shown on enlarged scale inFig. may be prepared in the usual way, with the addition that the shadedportions are treated so as to be opaque to ultra-violet light. Thistreatment should not affect the appearance of the "shaded portions? tothe eye so that the artist may visually obtain the desired shading whichhe desires to appear in the final reproduction. Furthermore, the shadedportions must maintain their relation to actinic visible light so thatthey may register selectively upon the negative in accordance with theirdensity on the original draw-- ing.

The most convenient way of making this orig-- inal drawing having theseoptical requirements. is to mix with the pigment employed by the artista material which is transparent to ordina light and which is opaque toultra-violet light. Thus,I may proceed, as far as the making of theoriginal drawing is concerned, in the manner described in my Patent No.2,191,939, issued February 27, 1940. As stated in that patent, Inlay usean ultra-violet absorbent substance, preierably of the fluorescent type,such as quinine bi sulfate. The quinine bisulfate is dissolved in we'-ter and the solution is used as a solvent for the water-color or inkpigment used to make the v Distilled water cc 1000 Quinine bisulfategrams 00 Sulphuric acid, C. P cc 10 Egg albumen, C. P grams 15 Thesulphuric acid amplifiesthe fluorescent and absorption properties. Theegg albumen facilitates the smooth application of the pigment to thedrawing. This solution is used instead of water as amedium for theartists pigment. The

pigment may be of any usual type; for example, it may be WindsorNewton's water-color Lampblack which is representative of the type ofmaterialcustomarily used in making wash drawings.

It will of course be understood that I 'do not intend to limit myapplication to quinine bisulfate since any other material, transparentto ordinary light and opaque to ultra-violet light, may be employed.Other materials which may be substituted for quinine blsulfate toprovide opacity to ultra-violet light include the following: anthracene,phenanthrene, various forms of naphthylamine disulphonic acid, beta.methyl umbelliierone, and para-hydroxy benzaldehyde.

The drawing is shown illustratively in Fig. 5,

" areas I; being highlights, area H being a light shaded" portion, areaI being a heavier shaded portion, area I8 being a line, and areas "beingtype" considered as line. The drawing will also include relatively largeareas of solid color (not shown) but the optical behavior, unlessadditional steps are taken, is the same for solid color as for line.

A part from the light which will be discussed hereinafter after. theprocedure of making the negative with the aid'of the artists drawing andemploying-my improved screen described above, may be effected in thenormal manner. Thus, the negative may be placed in a photoengravingcamera, my improved screen may be located in the camera at the properdistance ahead of the plate, and the drawing which is to be copied isplaced on a suitable support and illuminated by light. For

the purposes of the present, invention, the light must containultra-violet light and visible light. Suitably all the light is derivedfrom a single source which supplies both kinds of light. However, theinvention is not to be considered limited in this respect because twoseparate exposures may be made, one in which the positive is illuminatedby visible light, and another in which the positive is illuminated byultra-violet light. The result is the same in both cases.

Such a source for a visible light and ultra-violet light may suitably beany of the ordinary white-flame carbon arcs which radiate amply in theultra-violet region and also in the visible region. I may also use alamp manufactured by the General Electric Lompany oi.Los Angeles,California, which consists of a high-intensity 'mercurywaporargon-filled arc lamp in a double none}; or quartz nonex envelope. Lightrich in ultra-violet is generated by electronic disturbances between twobarium oxide coated cathode elements in the inner tube. The now popularmercury vapor lamps may also be used as an efiective light source.

Considering the ultra-violet light-lit will be understood that thepicture reflects no ultra -violet light from the line portions l6 andill, no ultravioletlight'irom "shaded portions id and it), and no lightfrom solid color portions. The highlight portions l3 reflect theultra-violet light and that ultra-violet light passes directly throughall portions of the screen corresponding thereto.

Thus, referring to Fig. (5,.it will be noted that the area of the screenincluding the lines it and it, as well as the open screen spaces betweenthe lines around the letter F, is completely transparent to ultra-violetlight. The same goes for the upper highlight portion 53 between the lineiii and the two shaded portions i l and it. It will therefore beunderstood that on the negative (Fig; 7) there are two portionscorresponding to the highlights it; which are completely exposed by theultra-violet light alone. By "completely exposed is meant that when thenegative is developed, there are two solid black portions constituted byreduced silver which portions correspond completely to the highlightsi3. It is to be noted that these portions corresponding to thehighlights l3 are completely devoid of screen pat tern because theexposure from the ultra-violet light alone is sufllcient completely toexpose the portions of the plate corresponding to these highlights.

Now to consider the action of the ultra-violet light upon the shadedportions l4 and l5-it will be noted that owing to the presence of anabsorbent for ultra-violet light, these two "shaded portions behave withrespect to that light precisely as if they were solid black. That is, noultra-violet light is reflected by the shaded portions" l4 and I5 (Fig.5) and consequently what ever screenv pattern is produced on thenegative corresponding to these areas results solely from the visiblelight or the visible component of the light. I

To consider the visible light or the visible component of the lightThevisible light striking the shaded areas" l5 and i5 is reflected therebyin amounts depending upon the degree of shading. Thus, the portion it!being slightly shaded, reflects strong visible light which strikesthescreen in the manner shown in Fig. 6.

Now, as has been described previously, the screen is areal operativescreen for visible light. The'lines W'of the screen are opaque tovisible" light and consequently the normal screen action occurs in thenegative (Fig, 'I). The light shaded" portion i l gives lalrgeoverlapping dots of reduced silver as shown in the upper left-handcorner of fig. 7, while the heavily shaded portion it gives small dotscorresponding to the openings in the screen as shown in the right-handtop corner of Fig. 7. Thus, the shaded portions print on the negative(Fig. 7) in the usual manner.

As has been previously pointed out; the visible light reflected by thehighlight portions it does not affect the corresponding portions of thenegative (Fig. 7) for the reason that the ultra-violet light reflectedfrom the highlight portions l3 passes through the corresponding portionsof the screen as if it were fully transparent. The visible lightreflected from the highlight portions l3 'may tsnd to form some screenpattern corresponding tothe highlights id but this tendency iscompletely destroyed owing to the fact that the ultra-violet lightcorresponding to the highlights i3 renders the corresponding portions ofthe negative (Fig. 7) completely black in the developed negative.

Qne outstanding effect of my invention is that the line and solid colorare not ragged around the edges due to encroachment on the "line" orsolid color of diffraction or lens action of the screen. Tl'ius,consider the line it and particularly the right-hand end of this line."It will be noted with reference to Fig. 6,

that this line passes across an opening in the screen. If we considerthiscpening, it will'be seen that a certain amount oi? visible lightfalls through it above and below the line it. It

- would be assumed that this opening would act as a lens and tend toform on the negative (Fig. 7) a black dot which would lie across thewhite image of the line ill on the egative. This dei initely dots notoccur in in cases and I attribute this result to the fact visible lightalone admitted through this opening, or rather the part of the openingreferred to which is obscured by the line it, is insuiificient toactivate the silver at this point. This dot-forming action or tendencyis not at all assisted by the ultra-violet light or the ultra-violetcomponent of the, light. Ultra-violet light finds the screen to bemerely a transparent plate so that the ultra-violet is not in the leastdifiracted.

Irrespective of whether or not this explanation'sets forth-the truecause of the result mentioned, the fact remains that fig. 7 is areproduction malny-times'enlarged of adrawing similar to Fig. and itwill be noted that perfect def initionof the "line" it and the "type" i?is obobtained in the metal printing elementderived therefrom.

Fig. 8 isan enlargement corresponding to Fig. 'I of a negative producedaccording to standard practice, the degree of enlargement being the samein both cases. The manner in which the fine line is lost and the sharpcontour of "type is completely obliterated, will readily'be seen fromFig. 8.

It is'apparent from the previous description that solid color isreproduced in the negative in exactly the same manner as the line." Themarginal definition of "solid color" is perfect and there is a completeabsence of screen pattern within the solid color. It is rreque'nthv anecessity for good printing that solid color" (and not line. or typefbshould be provided with screen pattern to a very slight degree toprevent subsequent deposit of excessive ink on "solid color".

areas when the finished plate is printed. This may be done by flashingthe "solid color areas, to

a' very slight extent. This flashing has no efliect' I upon" the "shadedportions because it merely re-' sults in the formation of small orincipient dots which are completely masked by the larger dots as aresult of normal exposure of the "shaded portions to the visibie lightor the visible comp'onentof the light. Ordinarily, however, it isimportant and desirable that the sharp definition of the line and theabsence therefrom of any encroachment of screen pattern should be verycarefully preserved.

Flashing may be effected simply by placing a layer of tissue paper overthe drawing of Fig. 5, and then drawing on. the tissu paper in black,matter corresponding .to the line" is and the "type II. This may be donequite roughly provided the roughlyapplied color does not overlie solidcolor portions of considerable size and in which it is desired to createscreen pattern. The

plate is then given a very small exposure with the lensstopped. down andwith visible light only.

- The degree of thisexposure is'merel sumcient to give a certain amountoi.'- screen pattern in the large solid color" portions. The tissuepaper is then removed and t e exposure of the negative is proceeded within he manner described above. Of course it is not to be deduced from theforegoing that it is necessary to do-the flashing before the exposuresince it will of coursebeclearly ap- -Although my invention has beendescribed in connectionwith specific detail o'f-the embodiments thereof,it must be understood that-the in-' vention is not intended to belimited thereto except in so far as set forth in the accompanyingclaims.

Having thus described my. invention, 1: declare that what I cla'imis:l'..In the art of halftone photo-reproduction,

the steps which consist in photographing a subject, theshaded portionsof whichhave been rendered absorbent of ultra-violet light, onto atained'in the negative and can of course be light-sensitive platethrough a halitone screen. the line elements of which are transparent toultra-violet light and substantially opaque to visible actinic light.

2. In the art of .halftone photo reproduction,

the steps of treating the shaded portions of matsorbent of ultra-violetlight, photo-graphicallytransferring light from said matter to alightsensitive. plate through a halitone screen havi line elementsopaque to visible actinic light and transparent to ultra-violet light.

4. In the art ofhalftonephoto-reproduction,

- the steps of including in the work areas oi a drawing to bereproduced, an absorbent of ultraviolet light, transferring ultra-violetand visible light from said drawing through a halftone screen onto alight-sensitive element, said halitone screen having line elementsopaque to visible actinic light but transparent to ultra-violet light.-

5. The method of photo-automatically producing a negative from a'pictorial representation,

which negative has highlights without screen not tern, shaded portionswith screen pattern, and line portions without screen pattern andwithout screen-pattern deformation, which consists inrendering the'workareas of said pictorial representation absorbent of ultra-violet light,and photographically exposing a plate to form the negative by means ofvisible actinic and ultraviolet light through a screen having lineelements opaque to actinic visible light and transparent to ultra-violetlight.

6. The. method of photo-automatically producinga negative from apictorial representatiom which negative has highlights without screenpattern, shaded portions with screen pattern, line portions withoutscreen pattern and withoutscreen-pattern deformation, and solid colorwith slight screen pattern, which consists in rendering the worlg areasof said pictorial representation absorbent of one kind of light,photographically exposing a plate to form the negative by means of saidkind oi. light and another kind of light through .a screen having lineelements opaque to last said kind of light and transparent to first saidkind of light, and flashing the negative slightly with the exception ofline portions.

Darent'to those skilled in the art that th order 0f exposure is quiteimmaterialr r tern, shaded portions with '7. The method ofphoto-automaticall producing-a negative from a pictorial representation,

which negative has highlights without screen paten pattern, lineportions without screen pattern and without screen-pattemdeformatiom-a'nd solid color with slight screen pattern, which consistsin rendering the work areas of said pictorial representation I absorbentof ultra-violet light, photogr'aphically exposing a plate to form thenegative by means of visible 'actinic and ultra-violet light through a fscreen. having line elements oqaque to actinic visible light andtransparent to ultra-violet light, I and flashing the-negative slightlywith the exoeption of line portions.

WALTER S.. MARX, Jn

